Most electrical switches, especially of the rotary type, have a mechanical detent to ensure a positive rest position for the switch contacts, to make it difficult to move the switch accidentally from a given position, to provide a tactile confirmation that the switch is in a desired position and, in some cases, to provide audible confirmation to the user, by the "click" produced by the detent, that a new position has been reached.
In most situations, these characteristics are desirable, or at least tolerable. However, there are situations where one or more of them, especially the audible "click", is either annoying or actually detrimental to the situation which requires the switch to be changed. One such situation occurs during the testing of hearing loss in hearing impaired individuals. An astute subject can pick up clues as to switch setting from the clicking noises made as the switch is moved and, consciously or unconsciously, give an incorrect response to the test. However, in this same case, it is highly desirable that the operator of the test have a non-visual--that is, tactile--confirmation of switch operation.
No existing switch offers a combination of good tactile detent operation, noiseless operation of both the switching action and the detent, and ability to distinguish between clockwise and counter-clockwise rotation. Brebbia et al U.S. Pat. No. 3,597,714 discloses a magnetically actuated rotary switch, in which an annularly-shaped permanent magnet, with multiple poles radially spaced on the surface thereof, is placed opposite to a second annularly-shaped permanent magnet with multiple poles similarly placed, providing a detent action as one magnet is rotated past the other. The opposite face of the second annularly-shaped permanent magnet incorporates thereon shaped, magnetized zones whose radial position varies in one or more places. Small permanent magnets mounted on snap-acting switches which are placed within the magnetic influence of the shaped magnetized zones act in accordance with the radial deviations of the magnetized zones causing the switches to operate as the second annularly-shaped permanent magnet is rotated with respect to the switches. The snap acting switches would have a characteristic clicking or snapping sound as the mechanism was operated.
Lau U.S. Pat. No. 4,054,944 discloses a pushbutton type switch, in which a magnet is used to obtain a mechanical behavior similar to a non-magnetic mechanical switch. In addition to a characteristic tapping or clicking sound as the contacts came together, this switch has a different structure than the present invention.
Paulet U.S. Pat. No. 4,199,741 discloses a magnetic switch in which the switching behavior is accomplished by moving magnets actuating the switching elements in response to magnetic poles which are brought close to, or taken away from, the moving magnets as the switch body is rotated about an axis. The movement of the permanent magnets would likely produce noise which might be detected by the subjects being tested.
Lerner et al U.S. Pat. No. 4,353,049 discloses a magnetically actuated reed switch which rotates between two metallic walls in response to the rotation of a shaft attached to a knob. There would be a characteristic "slap" or "click" as the magnetic member contacted the two walls, in addition to the "snap" of the reed switch as it changed position.
None of the above disclosures is inherently noiseless in operation and would thus not qualify for use in situations where noiseless operations was needed in conjunction with a tactile indication of switch actuation.
Kenney U.S. Pat. No. 3,800,204 discloses a selector switch in which solid state switching devices are energized by admission of light to light sensitive trigger devices which actuate the switching devices. No provision is present for any tactile indication of switch operation.
Angersbach et al U.S. Pat. No. 3,995,156 discloses a photoelectrically sensitive device for determining the speed of rotation of a rotating member and the angular displacement thereof.
Edwards U.S. Pat. No. 4,146,970 discloses a detector for actuating a readout display for indicating the general direction of travel of an automobile.
Klein U.S. Pat. No. 4,326,128 discloses a rotary transmitter using photoelectric elements for minimizing fluctuation in transmitted signals due to inaccuracies in structure or assembly of the transmitter.
Cox et al U.S. Pat. No. 4,375,592 discloses a photoelectrically actuated encoder which utilizes one set of photodetectors spaced circumferentially from a second set of photodetectors a distance equal to one half of an increment of an incrementally divided rotating mask.
Although some of the above disclosures offer one or the other of the desirable features of a noiseless switch and a tactile detent, none of them offers both, nor could any of them be combined to obtain the novel structure of the present invention.